Image forming system including a first printer connected to a host computer and a second printer connected to the host computer via a switching device provided in the first printer

ABSTRACT

An image forming system includes a first image forming apparatus which can be connected to a host computer as an image data supplying source and also connected to a second image forming apparatus so that the host computer can be selectively and reliably connected to one of the first and second image forming apparatuses. The first image forming apparatus is connected to the host computer so as to print the image data provided from the host computer. The second image forming apparatus is operatively connectable to the host computer via the first image forming apparatus so as to print the image data sent from the host computer. A switching device is provided in the first image forming apparatus. The switching device switches a connection of the host computer so that one of the first image forming apparatus and the second image forming apparatus is operatively connected to the host computer.

This is a divisional of application Ser. No. 09/907,274 filed Jul. 17,2001, now U.S. Pat. No. 6,559,959 which is a divisional of applicationSer. No. 09/479,777 filed Jan. 7, 2000, now U.S. Pat. No. 6,301,014which is a divisional of application Ser. No. 08/922,579 filed Sep. 3,1997, now U.S. Pat. No. 6,025,924.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an image forming system and,more particularly, to an image forming system including a plurality ofimage forming apparatuses selectively connected to a host computer.

2. Description of the Related Art

Generally, an image forming apparatus such as a printer is connected toa personal computer to output image data or information on a recordingpaper. Typically, the personal computers are connected to a singleprinter so that the personal computer is connected to the printer on aone to one basis. A centronics interface is the most popular way toconnect a printer to a personal computer. Normally, the printer isconnected to the personal computer via a connector conforming to thecentronics standards.

There are many types of printers such as laser printers, inkjetprinters, etc. Additionally, there are also monochrome and color typesof printers. Demand for use of different types of printers with a singlepersonal computer has been increasing. A description will now be givenof a typical case in which a monochrome laser printer and a color inkjetprinter are available. If only the monochrome laser printer is connectedto a personal computer, the need for color printing cannot be satisfied.Thus, it is also desirable to have a color inkjet printer connected tothe personal computer. On the other hand, if only the color inkjetprinter is connected to the personal computer, although monochromeprinting can be performed as well as color printing by the color inkjetprinter, this does have its disadvantages. For example, monochromeprinting by a color inkjet printer has a disadvantage in that theprinting speed is much slower than that of the monochrome laser printer.Additionally, the image quality of monochrome printing performed by thecolor inkjet printer is much lower than that of the monochrome laserprinter. Accordingly, considering the fact that most printing operationsare require monochrome printing, it is preferable that the monochromeprinter also be connected to the personal computer.

In most cases, when two printers are commonly used with one personalcomputer, the user must change from one printer to the other printer bydisconnecting the centronics connector of one printer and connecting thecentronics connector of the other printer. This changing operation isvery inconvenient for the user.

In order to eliminate such inconvenience, a switching device 101 such asshown in FIG. 1 is commercially available. The switching device 101 isprovided with three connectors CN1, CN2 and CN3 so that a personalcomputer 102 and two printers 103 and 104 are interconnected via theswitching device 101. The switching device 101 is provided toselectively connect one of the printers 103 and 104 to the personalcomputer 102 by control of the personal computer 102. Accordingly, theswitching device 101 is intended to eliminate the disconnecting andconnecting operations of the connectors of the printers 103 and 104.However, the switching operation performed by the switching device 101lacks reliability at the present time. This may be caused by poorcompatibility between the personal computer 102 and printers 103 and104. More specifically, although the personal computer 102 and theprinters 103 and 104 have an interface conforming to the centronicsstandard, each of the interfaces may actually conform to various localstandards which are based on the centronics standard. This situationcreates a problem that a personal computer may not have compatibilitywith a particular printer. When the above-mentioned switching device 101is used, as viewed from the personal computer 102, it is notrecognizable as to what types of printers are connected to the switchingdevice 101.

In order to eliminate the above-mentioned problem with respect tocompatibility, the printers to be connected to the switching device 101must be limited to ones which are compatible with the personal computer102. Accordingly, the types of printers which can be connected to theswitching device 101 is limited. This results in poor reliability of theswitching function of the switching device 101. That is, since generallythe personal computer is not intended to be used with two printerdrivers, there may be a case in which the printer is not operativelyconnected to the personal computer. Additionally, even if the printers102 and 104 can be operatively connected to the personal computer 102via the switching device 101, the total length of the cables between thepersonal computer 102 and each of the printers 103 and 104 becomesexcessively long, resulting in an increased possibility of noiseintrusion. Further, the commercially available switching device 101 mayperform a switching operation which requires electrical power whichcannot be provided from the personal computer 102 via the connecter C1.That is, there may be a case in which the switching device 101 must bedirectly connected to an external power source.

In the above-mentioned case, the personal computer 102 described asbeing connected to the printers 103 and 104. However, one or both of theprinters 103 and 104 may be replaced by a multi-function imageprocessing apparatus such as a multi-function peripheral (MFP) devicewhich may include a facsimile function, a scanning function and aprinting function. This results in similar problems to those discussedabove.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedand useful image forming system in which the above-mentioned problemsare eliminated.

A more specific object of the present invention is to provide an imageforming system including a first image forming apparatus which can beconnected to a host computer as an image data supplying source and alsoto a second image forming apparatus so that the host computer can beselectively and reliably connected to one of the first and second imageforming apparatuses.

According to an aspect of the present invention, an image forming systemincludes as least one user device for providing image data to beprinted, the at least one user device selected from one of a group of ahost computer and a network. A first peripheral device is connected tothe at least one user device for receiving the image data from the atleast one user device and for processing the received image data. Asecond peripheral device is operatively connected to the at least oneuser device via the first peripheral device for processing image datasent from the at least one user device via the first peripheral device.A switching device is provided in and controlled by the first peripheraldevice. The switching device automatically switches the connection ofthe at least one user device so that one of the first peripheral deviceand the second peripheral device is operatively connected to the atleast one user device.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described hereinbelow with reference to the accompanying drawings, wherein;

FIG. 1 is an illustration of a conventional image forming system using aswitching device;

FIG. 2 is an illustration of an image forming system according to afirst embodiment of the present invention;

FIG. 3 is an illustration of an entire system according to the firstembodiment of the present invention;

FIG. 4 is a flowchart of an operation performed by a personal computershown in FIG. 3;

FIG. 5 is a flowchart of an operation performed in a first printer shownin FIG. 3;

FIG. 6 is an illustration of a dialog window displayed on a personalcomputer provided in an image forming system according to a secondembodiment of the present invention;

FIG. 7 is an illustration of an operational panel of a printer providedin an image forming system according to a third embodiment of thepresent invention;

FIGS. 8A-8C are flowcharts of operations that can be performed by aprinter provided in the image forming system according to embodiments ofthe present invention;

FIG. 9 is a flowchart of an operation performed by a printer provided inan image forming apparatus according to a fourth embodiment of thepresent invention;

FIG. 10 is a flowchart of an operation performed by a printer providedin an image forming apparatus according to a fifth embodiment of thepresent invention;

FIG. 11 is an illustration of an image forming system according to asixth embodiment of the present invention;

FIG. 12 is a block diagram of a multi-function peripheral device shownin FIG. 11;

FIG. 13 is a circuit diagram of a switching device shown in FIG. 11;

FIG. 14 is a flowchart of an operation of a personal computer shown inFIG. 11;

FIG. 15 is a flowchart of an operation of an MFP device shown in FIG.11; and

FIG. 16 is a circuit diagram of a switch shown in FIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to FIGS. 2 to 5, of afirst embodiment of the present invention. FIG. 2 is a circuit diagramof a printer interface switching device of a monochrome laser printerincluded in an image forming system according to the first embodiment ofthe present invention.

The monochrome laser printer 1 shown in FIG. 2 is connected to a colorinkjet printer 2 and also connected to a personal computer 3. That is,the personal computer 3 and two printers 1 and 2 together constitute theimage forming system according to the present invention. Hereinafter,the monochrome laser printer 1 is referred to as a first printer, andthe color inkjet printer 2 is referred to as a second printer.

In the image forming system according to the present invention, thepersonal computer 3 is connected to the second printer 2 via the firstprinter 1 as shown in FIG. 3. The first printer 1 is provided with theprinter interface switching device 4 having a switching function. Theprinter interface switching device 4 is basically an interfaceconforming to the centronics standard.

The printer interface switching device 4 is provided with a firstconnector 5 and a second connector 6. The first connector 5 is connectedto a centronics standard connector of the personal computer 3. Thesecond connector 6 is connected to a centronics standard connector ofthe second printer 2. Since the printer interface switching device 4 isincorporated into the first printer 1, the printer interface switchingdevice 4 is connected to an electrical circuit of the first printer 1 byan internal wiring system in the first printer 1. Accordingly, there isno printer connector needed for the connection of the first printer 1.

The first printer 1 comprises therein a controller 8 including a centralprocessing unit (CPU) 7. The connector 5 is connected to the controller8 by a first printer signal transmission path 9. The first printersignal transmission path 9 comprises an eight-wire data bus 9 a, afour-wire reception control line 9 b and a five-wire transmissioncontrol line 9 c. Additionally, the connector 6 is connected to thecontroller 8 by a second printer signal transmission path 10. The secondprinter signal transmission path 10 comprises a data bus 10 a, areception control line 10 b and a transmission control line 10 c whichare branched from the data bus 9 a, the reception control line 9 b andthe transmission control line 9 c, respectively.

A switching unit 11 is provided to select one of the printer signaltransmission paths 9 and 10 in response to a switching signal providedby the controller 8. The switching unit 11 comprises buffers 12 a, 12 b,12 c, 13 b and 13 c and a switch 14. The buffers 12 a, 12 b and 12 c canbe set to either an active state or an inactive state, and are providedon the data bus 9 a, the reception control line 9 b and the transmissioncontrol line 9 c, respectively. The buffers 13 b and 13 c can be set toeither an active state or an inactive state, and are provided on thereception control line 10 b and the transmission control line 10 c,respectively. The switch 14 is controlled to be turned on or off, and isprovided on the data bus 10 a. The buffer 12 a is a bidirectionalbuffer.

The buffer 12 a is connected to the controller 8 via a control line 15 aso as to provide a switching signal which controls the operational stateof the buffer 12 a. The buffers 12 b and 13 b are connected to thecontroller 8 via the control line 15 b so as to provide a switchingsignal which selectively sets one of the buffers 12 b and 13 b to theactivated state. The buffers 12 c and 13 c are connected to thecontroller 8 via the control line 15 c so as to provide a switchingsignal which selectively sets one of the buffers 12 c and 13 c to theactivated state. The switch 14 is connected to the controller 8 via acontrol line 15 d so as to provide a switching signal which controls theoperational state of switch 14. Additionally, inverters 16 b and 16 care provided to the control lines 15 b and 15 c connected to the buffers13 b and 13 c, respectively, so as to invert the switching signals onthe control lines 15 b and 15 c.

A power source 17 is provided to operate the switching unit 11. Power isprovided to the power source 17 from the controller 8 via a power sourceline 18, and also provided from the second printer 2 via a peripherallogic high (P.L.H.) line 19 of the second connector 6. The P.L.H. line19 is provided for checking whether power of the second printer 2 isturned on. Specifically, the centronics interface is provided with asmall current from the second printer 2. Since diodes 20 and 21 areprovided on the power source line 18 and the P.L.H. line 19,respectively, the two lines 18 and 19 are connected in a logic summingmanner.

When the first printer 1 is turned on, the switching signals provided tothe control lines 15 a, 15 b and 15 c are initially set to a high level,and the switching signal provided to the control line 15 d is initiallyset to a low level. In this state, since the buffers 12 a to 12 c are inthe active state, the switch 14 is turned off and the buffers 13 b and13 c are in the inactive state, and the first printer signaltransmission path 9 is set to be effective.

Additionally, the personal computer 3 has a function for selectivelydesignating one of the first printer 1 and the second printer 2. Thepersonal computer 3 also has a switching command sending function forselecting a printer driver based on the designated selection.Specifically, for example, when a printing operation for an applicationof a word processor is performed, the first printer 1 can beautomatically designated by selecting the printer driver for the firstprinter 1. Alternatively, when a printing operation for an applicationof a word processor is performed, the second printer 2 can beautomatically designated by selecting the printer driver for the secondprinter 2. This function is performed by a CPU (not shown in the figure)of the personal computer 3.

The first printer 1 includes, in addition to the CPU 7, a ROM fixedlystoring data such as programs and a RAM rewritably storing variousinformation. The CPU 7 performs various processes and controls inaccordance with the program data stored in the ROM 7. For example, inthe present embodiment, a determining function and a path stateswitching function are provided. The determining function determines,when a switching command is sent by the switching command sendingfunction performs by personal computer 3 which is used for selecting aprinter driver in accordance with the operation for designating theprinter performed on the personal computer 3 side, whether the switchingcommand designates the first printer 1 or the second printer 2.Additionally, the path state switching function switches the state ofpaths by operating the switching unit 11 so as to effect one of thefirst printer signal reception path 9 and the second printer signalreception path 10 in accordance with the result of the determinationmade by the determining function.

In the above-mentioned structure in which two printers 1 and 2 areconnected to the personal computer 3, when all power is turned on, thecontroller 8 changes the switching signals on the control lines 15 a, 15b and 15 c to the high level. The switching signal on the control line15 d is at the low level. Accordingly, the first printer signaltransmission path 9 is selected, resulting in an equivalent state wherethe first printer 1 is connected to the personal computer 3. Thus, aprinting operation can be performed by the first printer 1 by sendingcharacter print data, other data or signals. In this case, monochromeprinting can be provided with a high quality image and at a high-speed.

A description will now be given, with reference to FIGS. 3 and 4, ofswitching to the second printer 2 and switching back to the firstprinter 1. The flowchart shown in FIG. 4 is a procedure performed by thepersonal computer 3. In order to switch to a printer to be used, theprinter driver corresponding to the printer to be used is selected onthe personal computer 3 when a printing operation is performed in theword processor application. Accordingly, it is determined first, in stepS1, whether or not an operation for selecting the printer is performed.If it is determined that the operation for selecting is performed, it isthen determined, in step S2, whether or not to switch from the firstprinter 1 to the second printer 2. If the determination of step S2 isnegative, it is determined, in step S4, whether or not to switch fromthe second printer 2 to the first printer 1. On the other hand, if thedetermination of step S2 is affirmative, the routine proceeds to step S3where the personal computer 3 sends to the first printer 1 a switchingcommand which indicates to switch from the first printer 1 to the secondprinter 2.

If it is determined, in step S4, that the switching is to be from thesecond printer 2 to the first printer 1, the routine proceeds to stepS5. In step S5, the personal computer 3 sends to the first printer 1 aswitching command which indicates to switch from the second printer 2 tothe first printer 1. The process of steps S3 to S5 is performed as afunction of the switching command sending function performed in thepersonal computer 3.

According to the present embodiment, personal computer 3 executes aprogram which monitors the currently selected printer driver. If aprinter driver for driving printer 1 is selected, a command is sent toswitch to printer 1. On the other hand, if a printer driver for drivingprinter 2 is selected, a command is sent to switch to printer 2.

When a command is sent from the personal computer 3 to the first printer1 via the connector 5, the command is received in the CPU 7 of thecontroller 8. It is then determined, in step S6 of FIG. 5, whether ornot the command is a switching command for the printer. If it isdetermined that the command is the switching command, the switching unit11 is operated, in step S7, so as to switch from the present printer tothe other printer. That is, when the switching command is input and ifthe command represents a command for switching from the first printer 1to the second printer 2, the switching signal provided to the switchingunit 11 is changed from the high level to the low level. Thereby, thesecond printer signal transmission path 10 is effected. This state isequivalent to the state where only the second printer 2 is connected tothe personal computer 3. Thus, a printing operation is performed by thesecond printer by sending character image data or other necessary datato the second printer 2 via the second printer signal transmission path10. In this case, a multi-color printing can be provided. When viewingfrom the first printer 1, the character image data passes through thefirst printer to the second printer 2.

On the other hand, when the switching command is input and if thecommand represents a command for switching from the second printer 2 tothe first printer 1, the switching signal provided to the switching unit11 is changed from the low level to the high level. Thereby, the firstprinter signal transmission path 9 is effected. This state is equivalentto the state where only the first printer 1 is connected to the personalcomputer 3. Thus, a printing operation is performed by the first printerby sending character image data or other necessary data to the firstprinter 1 via the first printer signal transmission path 9. Accordingly,the process of step S6 is performed as the function of the determiningfunction, and the process of step S7 is performed as the function of thepath state switching function.

As mentioned above, according to the present embodiment, the firstprinter 1 itself has the connector function and the switching functionso that the printers 1 and 2 are connected to a single centronicsinterface line extending from the personal computer 3. That is, a systemcan be provided in which a remote switching control is performed by thepersonal computer 3. Especially, according to the present embodiment,since the system is constructed so that the first printer 1 is thecenter of the system by providing the switching function to theinterface unit of the first printer 2 which is one of the objects toswitch, at least all of the command system of the first printer 1 isknown. Thus, even if the command system of the second printer 2 isunknown, switching between the first printer 1 and the second printer 2can be reliably performed. Additionally, since the first printer itselfhas the switching function in the interface unit, the connection of thefirst printer 1 can be achieved by internal wiring without a connector.Thus, a length of wire or cable can be shorter than that of a case inwhich a separate switching device 101 is used. This improves antinoisecharacteristics. Further, since the first printer 1 has the switchingdevice therein, a power source for the switching device can be the powersource for the first printer 1. That is, a separate power source is notneeded as in the case of the conventional switching device 101.

A description will now be given, with reference to FIG. 6, of a secondembodiment of the present invention. An image forming system accordingto the second embodiment is similar to that of the above-mentioned firstembodiment except for a dialog program being provided in the personalcomputer 3 as a means for designating one of the first printer 1(internal printer) and the second printer 2 (external printer). FIG. 6shows a dialog window 32 for designating one of the internal printer andthe external printer. Before starting a printing operation, the dialogwindow 32 is displayed, and a user can select one of the internalprinter and the external printer by moving a pointer or cursor 33 by amouse or similar cursor control means. When one of the internal printerand the external printer is selected in the dialog window 32, theswitching command is sent from the personal computer 3 to the firstprinter 1 similar to the process of steps S3 and S5 shown in FIG. 4.Then, the process of steps S6 and S7 shown in FIG>5 is performed in thefirst printer 1.

Thus, according to the present embodiment, the first printer itself hasthe connector function and the switching function so that the twoprinters 1 and 2 are connected to the personal computer 3 via a singlecentronics interface line extending from the personal computer 3. Thatis, a system can be provided in which a remote switching control isperformed by the personal computer 3.

A description will now be given, with reference to FIGS. 7 and 8A-8C, ofother embodiments of the present invention. An image forming systemaccording to these embodiments is similar to that of the above-mentionedfirst embodiment except for an operational panel 34 shown in FIG. 7being provided on the first printer 1. The operational panel 34 has aprinter designating part 35 for designating the printer to be used.Since the operational panel 34 is provided on the first printer 1, theprinter designating part 35 is operated only when the second printer 2is to be used. For example, the printer designating part 35 can be inthe form of a key for inputting a command to switch to the secondprinter. Thus, the first printer 1 is always monitoring whether or notthe printer designating part 35 is operated as indicated by step S11 ofthe flowchart of FIG. 8A. When it is determined that the printerdesignating part 35 is operated, the state of the switching signal ischanged, in step S12, so that the second printer signal transmissionpath 10 is effected. The process of step S12 is performed as thefunction of the path state switching function which switches the stateof the path so as to effect one of the first printer signal transmissionpath 9 and the second printer signal transmission path 10 in response tothe operation of the printer designating part 35.

Of course, variations of the embodiment depicted in FIG. 8A arepossible. As shown in FIG. 8B, when it is detected in step S11 that theprinter designating part 35 has been operated, a determination is madein step S11A whether the system is idle (e.g., whether the printer 1 iscurrently printing). The system waits until the system is idle (Yes instep S11A) and then switched to the printer 2 in step S12. In addition,as described with respect to FIG. 8A, if the printer 2 is currentlyselected, if it is determined in step S11 that a printer designatingoperation has again been performed (e.g., a user desires to switch backto the printer 1), the switching operation can proceed immediately tostep S12 for switching back to the printer 1. In the alternative, asshown in FIG. 8C, if it is determined in step S11 that the printerdesignating operation has again been performed (e.g., the user desiresto switch back to the printer 1), a determination is made in step S11Awhether the system is idle. If the system is not idle, (e.g., printer215 is currently printing), a warning can be issued in step S11B. Thewarning can be issued to the user by displaying a message indicationthat the printer 2 is currently printing and the printer 1 can not beselected. If the system is idle, the process proceeds to step S12 and aswitching command is issued.

The determination of whether the system is idle can be made bycontroller 8 by controlling bidirectional buffer 12 a so as to monitorthe data on the data bus 9 a. Thus, a determination can be mode by theprinter 1 that the system is busy, even if the printer 2 is thecurrently selected printer.

Thus, according to the present embodiment, the first printer itself hasthe connector function and the switching function so that the twoprinters 1 and 2 are connected to the personal computer 3 via a singlecentronics interface line extending from the personal computer 3. Thatis, a system can be provided in which a switching control can beperformed by an operation of the printer designating part 35.

A description will now be given, with reference to FIG. 9, of a fourthembodiment of the present invention. In the present embodiment, the CPU7 performs the processes corresponding to the determining function andthe path state switching functions as follows. The determining functiondetermines a time for switching the printer by monitoring whether thestate where no command data is provided continues for a predeterminedtime period while the second printer signal transmission path 10 iseffective. Additionally, the path state switching function switches thestate of the path so as to effect the first printer signal transmissionpath 9 by operating the switching unit 11 when it is determined by thedetermining function that it is time for switching the printer. That is,the present embodiment automatically returns the system to a state wherethe first printer 1 is usable when the system is set to a state wherethe second printer 2 is usable. It should be noted that a switchingoperation to the second printer 2 may be performed in an appropriatemanner such as disclosed in one of the aforementioned embodiments.Additionally, the present embodiment is provided with a timer, which isstarted at a predetermined time and counts a clock signal, so as tospecify the predetermined time period for use of the determiningfunction.

Referring to FIG. 9, in the present embodiment, the CPU 7 alwaysmonitors the state of the printer interface switching device 4 so as todetermine, in step S21, whether or not the second printer signaltransmission path 10 is effective. This determination can be performedbased on the present state of the switching signal. If the system is inthe state where the first printer 1 is usable, there is no need toswitch the printer. If the system is in the state where the secondprinter 2 is usable, it is determined, in step S22, whether or not thecommand data signal is sent from the personal computer 3 to the printerinterface switching device 4. This determination can be performed bymonitoring data on the data bus 10 a, which data is sent from thepersonal computer 3 while the bidirectional buffer 12 a on the data bus9 a is continuously controlled in an active state. If command data issent while the system is in the state where the second printer isusable, a switching operation is not performed since the second printer2 is being used. On the other hand, if the command data is not sent inthe state where the second printer 2 is usable, the operation of a timer(not shown) is started in step S23. Then, it is determined, in step S24,whether or not the command data is sent. If it is determined that thecommand data is sent from the personal computer 3 to the printerinterface switching circuit 4 during the counting operation of thetimer, the routine is ended so that no switching operation is performedand the system is maintained in the state where the second printer isusable. On the other hand, in step S25, it is determined whether or notthe counting operation of the timer has terminated. When no command datais sent from the personal computer 3 until the counting operation hasterminated, the state of the switching signal provided to the switchingunit 11 is changed, in step S26, from the low level to the high level.Thereby, the first printer signal transmission path 9 is effected, andthe system is set to the state which is equivalent to a state where onlythe first printer 1 is connected to the personal printer 3. Accordingly,the process of steps S21 to S25 is performed as a function of thedetermining function, and the process of step S26 is performed as afunction of the path state switching function.

According to the present embodiment, the system is automaticallyreturned to the state where the first printer 1 is usable if the secondprinter 2 is not used for the predetermined continuous time period evenif the system is set to the state where the second printer 2 is usable.That is, since the system according to the present embodiment isconstructed as the first printer 1 is the center of the system, thestate where the first printer 1 is usable is given priority. Thiscondition facilitates the control of the system, over the state wherethe second printer 2 is usable by automatically setting the firstprinter signal transmission path 9 to be effective.

A description will now be given, with reference to FIG. 10, of a fifthembodiment of the present invention. In the present embodiment, the CPU7 performs the processes corresponding to the determining function andthe path state switching function as follows. The determining functiondetermines, when a command is sent from the personal computer 3, whetheror not the command conform to the system command. The path stateswitching function changes the state of the path so as to effect thesecond printer signal transmission path 10 when it is determined that anunreadable command is sent from the personal computer 3 while the firstprinter signal transmission path 9 is effective. On the other hand, thepath state switching function changes the state of the path so as toeffect the first printer signal transmission path 9 when it isdetermined that a readable command is sent from the personal computer 3while the second printer signal transmission path 10 is effective. Itshould be noted that a FIFO buffer is provided in the RAM of thecontroller 8 so as to temporarily store information provided by thepersonal computer 3.

In the present embodiment, when the command is sent from the personalcomputer 3 to the printer interface switching device 4, the command istaken by the CPU 7 of the controller 8 via the bidirectional buffer 12 aon the data bus 9 a. It is then determined, in step S31, whether or notthe command is readable by the CPU 7. If the command is designated forthe first printer 1, the command must be readable by the CPU 7. Thus, inthis case, it is determined, in step S32, whether or not the firstprinter signal transmission path 9 is effective. If it is determined, instep S31, that the command is not readable by the CPU 70, the routineproceeds to step S34 where it is determined whether the second printersignal transmission path 10 is effective. If it is determined that thesecond printer signal transmission path 10 is effective, the routineproceeds to step S35. In step S35, the switching signal provided to theswitching unit 11 is changed from the low level to the high level sothat the first printer signal transmission path 9 becomes effective. Onthe other hand, if it is determined, in step S31, that the command fromthe personal computer 3 is not readable by the CPU 7, this means thatthe command is not designated for the first printer 1, and the routineproceeds to step S32. In step S32, it is determined whether or not thefirst printer signal transmission path 9 is effective. If it isdetermined that the first printer signal transmission path 9 is noteffective, that is, the second printer signal transmission path 10 iseffective, the routine is ended. On the other hand, if it is determined,in step S32, that the first printer signal transmission path 9 iseffective, the switching signal provided to the switching unit 11 ischanged from the high level to the low level so that the second printersignal transmission path 10 becomes effective.

As mentioned above, in the present embodiment, a different operation isperformed based on the determination of whether the command sent fromthe personal computer 3 is readable or unreadable. When the command isreadable, it is interpreted that the command is designated for the firstprinter 1, and the first printer signal transmission path 9 ismaintained effective or changed to be effective. On the other hand, ifthe command is unreadable, it is interpreted that the command isdesignated for the second printer, and the second printer signaltransmission path 10 is maintained effective or changed to be effective.It should be noted that the process of step S31 is performed as afunction of the determining function, and the process of steps S32 toS35 is performed as a function of the path state switching function.

It should be noted that, in the present embodiment, the command sentfrom the personal computer 3 is subjected to a reading operation by theCPU 7, and simultaneously stored in the FIFO buffer. Then, if thecommand is not readable by the CPU 7, the command temporarily stored inthe FIFO buffer is sent to the second printer 2 through the secondprinter signal transmission path 10. If the FIFO buffer is not provided,the command which was received and interpreted as not readable is lost,and the command cannot be sent to the printer 2.

According to the present embodiment, since the switching function forthe printers is provided in the interface unit of the first printer 1,the first printer 1 is located in the center of the system. Thus, takinginto consideration that the command system of the first printer isknown, if the command is not readable, this does not assure that thecommand is designated for the printer 2 but it can be interpreted thatthe command is at least not designated for the printer 1 and theswitching operation is performed. Thus, the switching of the printerscan be appropriately performed by utilizing the command itself.

A description will now be given of a sixth embodiment of the presentinvention. FIG. 11 is an illustration of an entire image forming systemaccording to the sixth embodiment of the present invention. In thissystem, a multi-function peripheral (MFP) device 51 and a secondperipheral device 72 are used instead of the first printer 1 and thesecond printer 2 in the above-mentioned embodiments, respectively. TheMFP device 51 has an interface switching device 73 which includes afirst connector 74 and a second connector 75. A personal computer 71 isconnected to the MFP device 51 via the first connector 74. The secondperipheral device 72 is connected to the MFP device 51 via the secondconnector 75. A facsimile line 54 is connected to the MFP device 51.

FIG. 12 is a block diagram of the MFP device 51 shown in FIG. 11. TheMFP device 51 comprises a scanner unit 52, a printer unit 53, a networkcontrol unit (NCU) 55, a modem 56, an image memory 57, a centralprocessing unit (CPU) 58, a memory 59, an operational unit 60, the firstconnector interface 74 and the second connector interface 75 which areinterconnected by a bus line 61.

The scanner unit 52 scans an original image and outputs image datacorresponding to the original image. The printer unit 53 outputs animage on a recording sheet according to image data supplied thereto. TheNCU 55 corresponds to a facsimile communication unit which transmits andreceives data through the facsimile line 54. The image memory 57 storesthe image data generated by the scanner unit 52 or image data receivedby the NCU 55. The operational unit 10 is provided for inputting variousinstructions to control the MFP device 51. Thus, the MFP device 51 has ascanner function, a printer function and a facsimile function.

The scanner unit 52 is a sheet scanner which scans images of originaldocuments fed by an automatic document feeder (ADF) (not shown in thefigure) by a contact-type optoelectric conversion element fixedlyprovided at a scanning position. Thus the original image is read andelectrical signals corresponding to the original images are generated.The printer unit 53 prints on a recording sheet based on digital imagedata. The printer unit 53 comprises, for example, a laser printer whichincludes a monochrome laser writing system and an electrophotographicdevice. The memory 59 comprises a ROM for fixedly storing data such asprograms and a RAM for rewritably storing various types of information.The CPU 8 performs various processes and controls in accordance with theprograms stored in the ROM.

As mentioned above, the MFP device 51 together with the personalcomputer 71 and the second peripheral device 72 are components of animage forming system in which the personal computer 71 can be connectedto one of the MFP device 51 and the second peripheral device 72. In thepresent embodiment, the second peripheral device 72 is a color inkjetprinter which has a printing capability different from that of theprinter unit 53 of the MFP device 51. Hereinafter, the second peripheraldevice 72 may be referred to as a second printer 72.

The personal computer 71 is connected to the second printer 72 via theMFP 1. Thus, the MFP 1 is provided with the interface switching device73 which has a switching function. Basically, the interface switchingdevice 73 conforms to the centronics standard.

FIG. 13 is a circuit diagram of the switching device 73. In FIG. 13,parts that are the same as the parts shown in FIG. 2 are given the samereference numerals.

The switching device 73 is provided with a first connector interface 74and a second connector interface 75. The first connector interface 74 isconnected to a centronics standard connector of the personal computer71. The second connector interface 75 is connected to a centronicsstandard connector (not shown in the figure) of the second printer 72.Since the switching device 73 is incorporated into the MFP device 51,the switching device 73 is connected to the electrical circuit of theMFP device 73 by an internal wiring system in the MFP device 51.Accordingly, there is no printer connector needed for the connection ofthe MFP device 51.

The MFP device 1 comprises a controller 76 including the centralprocessing unit (CPU) 58. The first connector interface 74 is connectedto the controller 76 by a first printer signal transmission path 9. Thefirst printer signal transmission path 9 comprises an eight-wire databus 9 a, a four-wire reception control line 9 b and a five-wiretransmission control line 9 c. Additionally, the second connectorinterface 75 is connected to the controller 76 by a second printersignal transmission path 10. The second printer signal transmission path10 comprises a data bus 10 a, a reception control line 10 b and atransmission control line 10 c which are branched from the data bus 9 a,the reception control line 9 b and the transmission control line 9 c,respectively.

A switching unit 11 is provided so as to effect one of the printersignal transmission paths 9 and 10 in response to a switching signalprovided by the controller 76. The switching unit 11 comprises buffers12 a, 12 b, 12 c, 13 b and 13 c and a switch 14. The buffers 12 a, 12 band 12 c can be set to either an active state or inactive state, and areprovided on the data bus 9 a, the reception control line 9 b and thetransmission control line 9 c, respectively. The buffers 13 b and 13 ccan be set to either an active state or inactive state, and are providedon the reception control line 10 b and the transmission control line 10c, respectively. The switch 14 is controlled to be turned on or off, andis provided on the data bus 10 a. The buffer 12 a is a bidirectionalbuffer.

The buffer 12 a is connected to the controller 76 via a control line 15a so as to provide a switching signal which controls the operationalstate of the buffer 12 a. The buffers 12 b and 13 b are connected to thecontroller 76 via the control line 15 b so as to provide a switchingsignal which selectively sets one of the buffers 12 b and 13 b to theactivated state. The buffers 12 c and 13 c are connected to thecontroller 76 via the control line 15 c so as to provide a switchingsignal which selectively sets one of the buffers 12 c and 13 c to theactivated state. The switch 14 is connected to the controller 76 via acontrol line 15 d so as to provide a switching signal which controls theoperational state of switch 14. Additionally, inverters 16 b and 16 care provided to the control lines 15 b and 15 c connected to the buffers13 b and 13 c, respectively, so as to invert the switching signals onthe control lines 15 b and 15 c.

A power source 17 is provided to operate the switching unit 11. Power isprovided to the power source 17 from the controller 76 via a powersource line 18, and also provided from the second printer 2 via aperipheral logic high (P.L.H.) line 19 of the second connector interface75. The P.L.H. line 19 is provided for checking whether power of thesecond printer 2 is turned on. Specifically, the centronics interface isprovided with a small current from the second printer 2. Since diodes 20and 21 are provided on the power source line 18 and the P.L.H. line 19,respectively, the two lines 18 and 19 are connected in a logic summingmanner.

When the MFP device 51 is turned on, the switching signals provided tothe control lines 15 a, 15 b and 15 c are initially set to a high level,and the switching signal provided to the control line 15 d is initiallyset to a low level. In this state, since the buffers 12 a to 12 c are inthe active state, the switch 14 is turned off and the buffers 13 b and13 c are in the inactive state, the first printer signal transmissionpath 9 is set to be effective.

Additionally, the personal computer 71 has a function for selectivelydesignating one of the MFP device 51 and the second printer 72. Thepersonal computer 71 also has a switching command sending function forselecting a printer driver based on the selective designation.Specifically, for example, when a printing operation for an applicationof a word processor is performed, the MFP device 51 can be automaticallydesignated by selecting the printer driver for the MFP device 51.Alternatively, when a printing operation for an application of a wordprocessor is performed, the second printer 72 can be automaticallydesignated by selecting the printer driver for the second printer 72.This function is performed by a CPU (not shown in the figure) of thepersonal computer 71.

In the MFP device 51, the CPU 58 performs various processes and controlsin accordance with the program data stored in the ROM of the memory 59.In the present embodiment, a determining function, a path stateswitching function and a concurrent printing function are provided. Thedetermining function determines, whether the switching commanddesignates the MFP device 51 or the second printer 72, when theswitching command is sent by the switching command sending function soas to select the printer driver in accordance with the operation fordesignating the printer by the personal computer 71. Additionally, thepath state switching function switches the state of paths by operatingthe switching unit 11 so as to effect one of the first printer signalreception path 9 and the second printer signal reception path 10 inaccordance with the determination result of the determining function.Further, the concurrent printing function functions to provide imagedata generated by the scanner unit 52 of the MFP device 51 to both theprinter unit 53 and the second printer 72 so as to concurrently printthe image data by both the MFP device 51 and the second printer 72.

In the above-mentioned structure in which the MFP device 51 and thesecond printer 72 are connected to the personal computer 71, when allpower is turned on, the controller 76 changes the switching signals onthe control lines 15 a, 15 b and 15 c to the high level. The switchingsignal on the control line 15 d is at the low level. Accordingly, thefirst printer signal transmission path 9 becomes effective, resulting ina state where only the MFP device 51 is connected to the personalcomputer 71. Thus, a printing operation can be performed by the MFPdevice 51 by sending character print data, other data or signals. Inthis case, monochrome printing can be provided with a high quality imageat a high-speed. Additionally, the image data generated by the scannerunit 52 of the MFP device 51 can be sent to the personal computer 71 soas to store the image data in the personal computer 71.

A description will now be given, with reference to flowcharts shown inFIGS. 14 and 15, of a switching operation from the MFP device 51 to thesecond printer 2 and switching from the second printer 72 to the MFPdevice 51. In order to switch to a printer for a printing operation, theprinter driver corresponding to the printer to be used is selected bythe personal computer 71 when a printing operation is performed in theword processor application. Accordingly, it is determined first, in stepS51, whether or not an operation for selecting the printer is performed.If it is determined that the operation for selecting is performed, it isthen determined, in step S52, whether or not the switching is from theMFP device 51 to the second printer 72. If the determination of step S52is negative, it is determined, in step S54, whether or not the switchingis from the second printer 72 to the MFP device 51. On the other hand,if the determination of step S52 is affirmative, the routine proceeds tostep S53 where the personal computer 71 sends to the MFP device 51 aswitching command for switching from the MFP device 51 to the secondprinter 72.

If it is determined, in step S54, that the switching is from the secondprinter 72 to the MFP device 51, the routine proceeds to step S55. Instep S55, the personal computer 71 sends to the MFP device 51 aswitching command for switching from the second printer 72 to the MFPdevice 51. The process of steps S53 to S55 is performed as a function ofthe switching command sending function in the personal computer 71.

When a command is sent from the personal computer 71 to the MFP device51 via the connector interface 74, the command is received in the CPU 58of the controller 76. It is then determined, in step S56 of FIG. 15,whether or not the command is the switching command for the printer. Ifit is determined that the command is the switching command, theswitching unit 11 is operated, in step S57, so as to switch from the MFPdevice 51 to the second printer 72. That is, when the switching commandis input and if the command represents the switching from the MFP device51 to the second printer 72, the switching signal provided to theswitching unit 11 is changed from the high level to the low level.Thereby, the second printer signal transmission path 10 is effected.This state is equivalent to the state where only the second printer 2 isconnected to the personal computer 71. Thus, a printing operation isperformed by the second printer by sending character image data or othernecessary data to the second printer 72 via the second printer signaltransmission path 10. In this case, a multi-color printing can beprovided. When viewing from the MFP device 51, the character image datagoes through to the second printer 72.

On the other hand, when the switching command is input and if thecommand represents the switching from the second printer 72 to the MFPdevice 51, the switching signal provided to the switching unit 11 ischanged from the low level to the high level. Thereby, the first printersignal transmission path 9 is effected. This state is equivalent to thestate where only the MFP device 51 is connected to the personal computer71. Thus, a printing operation is performed by the MFP device 51 bysending character image data or other necessary data to the MFP device51 via the first printer signal transmission path 9. Accordingly, theprocess of step S56 is performed as the function of the determiningfunction, and the process of step S57 is performed as a function of thepath state switching function.

As mentioned above, according to the present embodiment, the MFP device51 itself has the connector function and the switching function so thatthe MFP device 51 and the second printer 72 are connected to a singlecentronics interface line extending from the personal computer 71. Thatis, a system can be provided in which a remote switching control isperformed by the personal computer 71. Especially, according to thepresent embodiment, since the system is constructed so that the MFPdevice 51 is the center of the system by providing the switchingfunction to the interface unit of the MFP device 51 which is one ofobjects to be switched, at least all of the command system of the MFPdevice 51 is known. Thus, even if the command system of the secondprinter 72 is unknown, switching between the MFP device 51 and thesecond printer 72 can be reliably performed. Additionally, as the MFPdevice 51 itself has the switching function in the interface unit, theconnection of the MFP device 51 can be achieved by internal wiringwithout a connector. Thus, a length of wire or cable can be shorter thanthat of a case in which a separate switching device is used. Thisimproves antinoise characteristics. Further, since the MFP device 51 hasthe switching device therein, a power source for the switching devicecan be the power source for the MFP device 51. That is, a separate powersource is not needed as in the case of the separate switching device.

A description will now be given of an operation for printing the imagedata generated by the scanner unit 52 of the MFP device 51. Since theMFP device 51 has the scanner unit 52 and the printer unit 53, the imagedata generated by scanning an original document by the scanner unit 52can be printed by the printer unit 53. This means that the MFP device 51includes a copying function. The MFP device according to the presentembodiment has an ability to print the image data generated by thescanner unit 52 by both the printer unit 53 of the MFP device 51 and thesecond printer 72 at the same time. This function is performed by theconcurrent printing function under the control of the CPU 58. When acopy mode is designated by the operational unit 60 in a printing modewhere a plurality of copies are printed, concurrent printing isperformed. That is, the controller 76 changes the switching signals onthe control lines 15 a and 15 d to the high level so that the data buses9 a and 10 a are effective to connect the controller 76 to the secondconnector interface 75. Thus, the MFP device 51 is connected to thesecond printer 72. In this state, when the scanner unit 52 scans anoriginal image and generates image data, the image data is sent to theprinter unit within the MFP device 51, and is simultaneously sent to thesecond printer 72 via the data busses 9 a and 10 a and the secondconnector interface 75. Accordingly, both the printer unit 53 and thesecond printer 72 print the image data at the same time. This achieves acircumstances in which the personal computer 71 is connected to twoprinters in parallel. Thus, since the printing operation of a pluralityof copies can be distributed to the two printers, that is, the printerunit 53 and the second printer 72, the printing operation for aplurality of copies can be performed at a high speed. The presentembodiment takes advantage of the fact that the personal computer 71 issubstantially connected to the two printers.

It should be noted that, as for the determining function and the pathstate switching function, the present invention is not limited to thatspecifically disclosed, and other appropriate determining and path stateswitching functions or units may be used.

A description will now be given of a seventh embodiment of the presentinvention. The structure of the seventh embodiment is basically the samewith that of the sixth embodiment, and a description will be given withreference to FIG. 13. In the present embodiment, the CPU 58 of the MFPdevice 51 performs a memory control function in addition to thedetermining function and the path state switching function. When theimage data sent from the personal computer 71 is printed by the secondprinter 72, the memory control function operates the image memory 57 asa printer buffer by connecting between the connector interface 74 andthe MFP device 51.

In the present embodiment, when a print mode is designated in which thesecond printer 72 is used to print image data generated by the personalcomputer 71, the second printer signal transmission path 10 is noteffective but the first printer signal transmission path 9 is turned onso as to be effective and provide the image data from the personalcomputer 71 to the image memory 57 of the MFP device 51 via theconnector interface 74 and the bidirectional buffer 12 a. The image datais then temporarily stored in the image buffer 57. The image data isthen sent to the second printer 72 via the data buses 9 a and 10 a byeffecting the data buses 9 a and 10 a between the controller 76 and theconnector interface 75. The data busses 9 a and 10 a are effected bychanging the switching signals on the control lines 15 a and 15 d to thehigh level. Accordingly, the image memory 57, which is originallyprovided for facsimile transmission, can be used as a buffer forprinting operation. This eliminates the need for using a buffer forprinting operations in the personal computer 71. Thus, there is no timeloss caused by the buffer in the personal computer 71. That is, thistakes advantage of the fact that the personal computer 71 is connectedto the MFP device 51 which has the image memory therein.

A description will now be given of an eighth embodiment of the presentinvention. A structure of the present embodiment is basically the sameas that of the seventh embodiment, and a description will be given withreference to FIG. 13.

In this embodiment, a scanner is used as the second peripheral device.That is, the scanner is used instead of the second printer 72.Hereinafter, the scanner is referred to as a second scanner 72. As forthe second scanner 72, for example, a color scanner or a high-resolutionscanner may be used. In the present embodiment, the CPU 58 of the MFPdevice 51 performs functions as an operation control function inaddition to the determining function and the path state switchingfunction. The operation control function is performed when the imagedata generated by the second scanner 72 is sent to the personal computer71. Specifically, the second connector interface 75 and MFP device 51are connected, and the image memory 57 is used as a date buffer so thatthe image data generated by the second scanner 72 is temporarily storedin the image memory 57.

In the present embodiment, when a print mode is designated in whichimage data generated by the second scanner 72 is sent to the personalcomputer 71, the data buses 10 a and 9 a are turned on so as to beeffective and the second scanner 72 is operatively connected to the MFPdevice 51 by changing the switching signals on the control lines 15 aand 15 d to the high level. Thus, the image data generated by the secondscanner can be temporarily stored in the image memory 57 in the MFPdevice 51 as a data buffer. That is, the image memory 57 serves as adata buffer similar to the manner when image data received by the NCU 55for facsimile communication is stored or image data generated by thescanner unit 52 is stored. Thereafter, the first print signaltransmission path 9 is turned on so as to be effective and tooperatively connect the MFP device 51 to the personal computer 71. Thus,the image data in the image memory 57 can be sent to the personalcomputer 71 via the data bus 9 a. Thereby, the image data generated bythe second scanner 72 can be sent to the personal computer 71 via theimage memory 57.

Accordingly, in the present embodiment, a high-speed reading operationcan be performed by the second scanner 72 since a delay in the operationspeed of the application can be eliminated as compared to a case inwhich the second scanner is directly connected to the personal computer71. Additionally, when the second scanner 72 is directly connected tothe personal computer 71, image data generated by the second scanner 72may be reduced so as to avoid a lack of capacity of a memory provided inthe personal computer 71. The reduction of image data is generallyperformed, for example, by intermittently eliminating image datagenerated by the scanner. Thus, in such a case, the image quality isdeteriorated even when a high-resolution scanner is used as the secondscanner 72. In this respect, according to the present invention, sincethe image memory 57 is used as a data buffer which is originally forfacsimile communication and has inherently a large capacity, there is noneed to reduce the amount of image data. Thus, the image quality can beimproved as compared to the case where the scanner is directly connectedto the personal computer 71. That is, the image reading capability ofthe scanner 72 is not deteriorated due to lack of memory capacity. Thisembodiment takes advantage of the fact that the second scanner 72 isconnected to the personal computer 71 via the MFP device 51 having theimage memory 57 therein.

A description will now be given of a ninth embodiment of the presentinvention. The basic structure and operation of the ninth embodiment isthe same as that of the first embodiment, and a description will begiven, with reference to FIG. 2, of structures and operations differentfrom that of the first embodiment.

In this embodiment, when the second printer is used, an ESC command issent by the personal computer 3. The ESC command comprises a printerselection code in accordance with an escape sequence. The controller 8receives the ESC command via the first printer signal transmission path,and the CPU 7 recognizes the reception of the command. Thus, the CPU 7changes the switching signals on the control lines 15 a to 15 c to thelow level, and changes the switching command on the control line 15 d tothe high level. Thereby, the buffers 13 b and 13 c are set to the activestate, and the switch 14 is closed so as to be turned on, resulting inthe second printer signal transmission path being effective.Accordingly, the system is set in a state equivalent to a state whereonly the second printer 2 is connected to the personal computer 3 viathe connectors 5 and 6. Thus, a printing operation can be performed bythe second printer 2 by sending from the personal computer 3 image data,character data or other data and signals. In this embodiment,multi-color printing can be performed.

On the other hand, in order to return the system to the state where thefirst printer 1 is usable, the personal computer 3 sends a printerinitialization signal (/INIT) to the printer interface switching device4 via the first connector 5. The printer initialization signal (/INIT)is a signal conforming to the centronics standard, and thus this signalis readable by the CPU 7. When the printer initialization signal (/INIT)is received, the CPU 7 operates the switching unit 11 to be returned tothe initial state after the power is turned on. Thus, the first printersignal transmission path 9 is turned on so as to be effective instead ofthe second printer signal transmission path 10. In such a switchingoperation, it is better to use a command readable by the second printer2. However, the command system of the second printer is unknown as faras the first printer 1 is concerned. Thus, the command system of thesecond printer 2 does not always conform to the command system of thefirst printer 1. Rather, in many cases, the command systems of the firstand second printers are different from each other. In such a case, if acommand conforming to the command system of the second printer is sentto the first printer 1, the command cannot be read by the CPU 7 of thefirst printer 1, and thus the switching operation from the secondprinter 2 to the first printer 1 cannot be performed. Accordingly, inthe present embodiment, the switching operation is performed by using acommand which is positively readable by the CPU 7 of the first printer1. Therefore, control of the first printer 1 and the second printer 2can be arbitrarily performed by the personal computer 3.

It is possible that a situation could occur in which the first printer 1is turned off and the second printer and the personal computer 3 areturned on. Even in such a situation, it is desirable that the secondprinter 2 can be usable by the personal computer 3. Since the printerinterface switching device 4 is incorporated into the first printer 1and the power of the first printer is turned off, the switching unit 11cannot be operated to switch the connection to the second printer 2 whenthe power is provided to the switching unit 11 only from the firstprinter 1. However, in the present embodiment, the power is provided tothe switching unit 11 from the second printer via the connector 6 andthe switching unit 11 can be operated when the second printer 2 isturned on. Additionally, in this embodiment, the second printer signaltransmission path 10 is effective even when the controller 8 of thefirst printer 1 does not operate due to the first printer 1 being turnedoff since the low level of the switching signal provided to theswitching unit 11 is set to a ground level which is provided when thefirst printer 1 is turned off. Accordingly, the second printer 2 can beoperatively connected to the personal computer even when the power ofthe first printer 1 is turned off.

A description will now be given, with reference to FIG. 16, of astructure and an operation of the switch 14 of FIG. 2. The switch 14 maybe a mechanical switch. However, it is preferable that the switch 14 isan analog IC switch 22 constructed by an integrated circuit. In thiscase, in order to protect the analog switch 22 from an external noise,protective diodes 23 a to 23 d are interposed between the input andoutput signal terminals and the power source as shown in FIG. 16.However, if only the protective diodes 23 a to 23 d are provided, astate of the power source of the switch 14 is equivalent to a statewhere the power source is grounded. Thus, it is possible that a reversecurrent could flow into the analog IC switch 22 via the signal line.This is not preferable since the reverse current may destroy the analogIC switch 22 which comprises an integrated circuit. Accordingly, in thepresent embodiment, in order to prevent the reverse current from flowinginto the analog IC switch 22, a diode 24 (correspond to the diode 20 inFIG. 2) is provided on the power source line 18 in a direction oppositeto the direction of the diodes 23 a to 23 d. Thus, even if the firstprinter 1 is turned off and the personal computer 3 is turned on, thereverse current does not flow into the analog IC switch 22 from thesignal line. Thus, the analog IC switch 22 is positively protected.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention. For example, althoughthe above-described embodiments refer to a host computer as providingthe data, any other type of user device as a network, for example, canprovide the data. In addition, although the embodiments refer to the useof printers or multi-functional peripherals, other types of peripheraldevices such as facsimile and scanner type device may be used.

What is claimed is:
 1. A host computer for connection to a firstperipheral device, said first peripheral device including a switch forselectively directing information received from said host computer to asecond peripheral device or to said first peripheral device forprocessing, said host computer comprising: a memory for storinginformation, said memory storing operating programs for performingoperations using said host computer and at least first and secondperipheral driver programs which when selected control said first andsecond peripheral devices, respectively; and a processor for processinginformation and for executing the operating programs stored in saidmemory, said processor executing an operating program for monitoringwhich of the first and second peripheral driver programs is selected,wherein when the first peripheral driver program is selected, saidprocessor sends data to the first peripheral device controlling theswitch so that information received from said host computer is directedto the first peripheral device for processing and when said secondperipheral driver program is selected, said processor sends data to thefirst peripheral device controlling the switch so that informationreceived from said host computer is directed to the second peripheraldevice for processing.
 2. A computer readable medium storing a programfor execution on a host computer, the host computer connecting to afirst peripheral device, said first peripheral device including a switchfor selectively directing information received from said host computerto a second peripheral device or to said first peripheral device forprocessing, said host computer storing operating programs for performingoperations using said host computer and at least first and secondperipheral driver programs which when selected control said first andsecond peripheral devices, respectively, said program performing stepscomprising: monitoring which of the first and second peripheral driverprograms is selected; sending data to the first peripheral devicecontrolling the switch so that information received from said hostcomputer is directed to the first peripheral device for processing whenthe first peripheral driver program is selected; and sending data to thefirst peripheral device controlling the switch so that informationreceived from said host computer is directed to the second peripheraldevice for processing when the second peripheral driver program isselected.